U.S. Pat. No. 3,765,689, assigned to Durametallic Corporation, discloses a mechanical seal construction employing an improved mounting arrangement for securing a face ring to a seal ring. As disclosed in this patent, the face ring is press fit into an annular recess formed at one end of the seal ring so that the face ring seats against an end surface of the seal ring. The seal ring has an annular axially-projecting flange which surrounds the external cylindrical periphery of the seal ring, which flange is suitably undercut to create an interference fit with the periphery of the face ring substantially at the central transverse plane thereof. This mounting arrangement minimizes twisting distortion of the face ring which, due to its construction from a hard and wear resistant material such as tungsten carbide, must be maintained in a substantialy nondistorted condition so that the flatness of the front seal face will be maintained.
The improved mounting arrangement of the aforesaid patent has proven highly successful in minimizing or at least reducing leakage past the relatively rotatable seal faces, particularly under conditions wherein the seal construction is used with low temperature fluids and the seal construction is of rather small diameter. However, under operating conditions wherein the seal construction is exposed to higher temperature fluids in the order of 350.degree. to 400.degree. F., or above, it has been observed that mounting the face ring in the manner disclosed by the aforesaid patent still results in twisting distortion of the face ring, and hence the flatness of the seal face is sufficiently destroyed as to permit undesired and sometimes unacceptable leakage between the relatively rotatable seal faces. Further, many industries are presently attempting to utilize mechanical seal contructions on larger pumps and the like used for handling high temperature fluids, and this in turn requires larger diameter seals. This has been observed to still further increase the amount of leakage between the seal faces, particularly when exposed to a high temperature fluid.
In addition to the problem of leakage across the seal faces, the industry trend toward utilizing larger seals under high temperature conditions has also resulted in many of these mechanical seal constructions being modified so as to incorporate a metal bellows in association therewith, inasmuch as such bellows is able to withstand both the high temperatures and the corrosive or chemical characteristics of the fluids without being degraded. Incorporation of a metal bellows into the mechanical seal construction, however, creates additional problems due to the fixation (as by welding) of the bellows to the seal ring, thereby making mounting of the face ring to the seal ring a more difficult endeavor.
Accordingly, it is an object of this invention to provide an improved mechanical seal construction employing an improved mounting between the face and seal rings, which mounting still creates an interference fit therebetween but substantially eliminates undesired distortion of the face ring, particularly when the seal construction is utilized with high temperature fluids and/or is of large diameter, so as to greatly minimize any leakage past the relatively rotatable seal faces.
A further object is to provide an improved seal construction, as aforesaid, wherein the interference fit between the seal and face rings results in the seal ring applying a radial holding force to the face ring substantially within the central transverse plane thereof to prevent imposition of distortion-causing moments on the face ring, which holding force defines the sole support and engagement between the face and seal rings.
Still a further object of this invention is to provide an improved seal construction, as aforesaid, wherein the seal ring has an annular flange surrounding at least a portion of the face ring, with the inner end of either the flange or face ring being undercut so that the flange engages the face ring substantially at, but only at, the central transverse plane thereof to thus impose a holding force on the face ring substantially only at, or at least adjacent, said plane, irrespective of the deflection of the flange as caused by the interference-fit engagement of the face ring within the flange. The inner axial end of the face ring is maintained spaced from, and hence not engaged with, the opposed end face on the seal ring to prevent the latter from imposing any distortion-causing moments on the face ring due to differential thermal expansion and/or residual contact or mounting stresses.
Another object of this invention is to provide an improved seal construction, as aforesaid, wherein the seal ring has a metal bellows fixedly joined to the end thereof opposite the face ring, and wherein the seal ring is also provided with internal and external tool-receiving grooves to facilitate the secure support of the seal ring to permit removal and replacement of a damaged face ring.
Other objects and purposes of the invention will be apparent upon reading the following specification and inspecting the accompanying drawings.
The objects and purposes of the invention are met by providing an improved mechanical seal construction for sealing a shaft which is relatively rotatable with respect to a wall. The seal construction has a first annular element which is nonrotatably secured relative to the wall, and a second annular element which is nonrotatably mounted relative to the shaft, these elements having opposed seal faces which are resiliently urged into sealing and rotatable sliding engagement with each other. One of the annular elements includes a seal ring having holding structure associated therewith for nonrotatably mounting a face ring by means of an interference fit. The holding structure includes an annular flange which projects axially from one end of the seal ring and defines an annular recess into which the face ring is interference fitted. The flange and face ring have an annular clearance therebetween adjacent the inner ends thereof, so that the flange exerts a radially inwardly-directed holding force around the periphery of the face ring, which holding force is disposed substantially within the central plane of the face ring. The inner end of the face ring is also axially spaced from the opposed end surface on the seal ring, whereby the face ring is supported on and engaged with the seal ring solely by the flange and the holding force imposed substantially along the central plane.